1. Field of the Invention
The present invention relates to an encoder having a function for detecting an amount of noise which may affect an internal signal of the encoder.
2. Description of the Related Art
In the prior art, in order to measure an amount of noise in an encoder, it is necessary to arrange a device adapted to measure noise outside the encoder, or arrange a dedicated circuit adapted to measure noise within the encoder. For example, FIG. 12 of Japanese Unexamined Patent Publication (Kokai) No. 2005-172523 discloses a configuration having a voltage measuring means 104 adapted to measure a noise potential between a motor housing 13 and a circuit board (0V) within an encoder.
Further, FIG. 1 of Japanese Unexamined Patent Publication (Kokai) No. 2005-172523 discloses an encoder 1 having a detecting means 2 adapted to detect the movement of a movable body 10, a signal processing circuit 3 adapted to process a detection signal from detecting means 2 and output an encoder signal, and a noise detecting means 4 adapted to detect a noise component included in the detection signal, wherein detection means 2, signal processing means 3 and noise detecting means 4 are incorporated in the same apparatus. In encoder 1, a noise level may be determined by means of a coupling condenser adapted to extract an AC component from the detection signal and an A/D converting circuit adapted to determine the noise level based on the extracted AC component.
In the configuration as shown in FIG. 12 of Japanese Unexamined Patent Publication (Kokai) No. 2005-172523, it is necessary to arrange the voltage measuring means outside of the encoder, in order to measure the noise potential of the encoder. Therefore, it is difficult to always measure the noise potential.
On the other hand, when the dedicated circuit for measuring the noise is arranged within the encoder, the encoder is enlarged and the cost thereof is increased.